I might be late for this, but recently 3 characters have been added into Sonic Runners. They are:
Silver is a Speed type, Cream is a Fly type and Big is a Power type. All of them are actually under one team:Team Easy. If you're playing as any of these members, your speed is reduced by 10% and your score rate is cut in half, thus making them the worse team in the game.
How to Purchase
Unlike other characters(excluding Tails and Knuckles), they are actually more easier to unlock. Instead of the roulette, you can purchase them directly with 250 Red Star Rings or 5,000,000 Rings. They might cause a lot, but it is way better than the roulette. So why not give them a try? ¯\_(ツ)_/¯